A television broadcast receiving apparatus often adopts a method of mixing a local oscillation signal, that is created in a PLL or the like, with a received radio-frequency signal so as to perform frequency conversion so that the received signal is converted to an intermediate frequency signal or a base band signal. This manner offers relatively easy production of a base band signal.
FIG. 5 is a block diagram illustrating an electrical structure of a typical conventional radio-frequency receiving apparatus (hereinafter it may be simply referred to as a receiving apparatus) 1 performing such frequency conversion. The receiving apparatus 1 performs reception of digital television broadcasts. A radio-frequency signal (quadrature digital modulation signal) transmitted from a TV station is inputted to the receiving apparatus 1 via an input terminal 2. Then, the input radio-frequency signal is supplied to a gain-variable radio-frequency amplifier 3 to be amplified, before commonly supplied to two mixers 4 and 5. The separated two input radio-frequency signals supplied to the mixers 4 and 5 are respectively mixed with local oscillation signals of 0° and 90° phases, to be modulated to quadrature base band signals I and Q.
The base band signal outputted from the mixer 4 is amplified at a gain-variable base band amplifier 6. Then, a low-pass filter 7 extracts a frequency component of the desired band from the base band signal. Thereafter, the base band signal is further amplified at the amplifier 8 before outputted via a base band output terminal 9.
Similarly, the base band signal outputted from the mixer 5 is amplified at a gain-variable base band amplifier 10, and then a low-pass filter 11 extracts a frequency component of the desired band from the base band signal. Thereafter, the base band signal is further amplified at the amplifier 12 before outputted via a base band output terminal 13.
The receiving apparatus 1 includes a voltage-control-type local oscillator (VCO) 14, an oscillator 15, a PLL (Phase Lock Loop) circuit 16, and a 90° phase shifter 17. The local oscillation signal produced at the VCO 14 passes through the 90° phase shifter 17 to be supplied to one of the mixers 4 and 5. One of the mixers (the mixer 4 in FIG. 5) is supplied with a 0° component, i.e., an unmodified signal, and the other (the mixer 5 in FIG. 5) is supplied with a 90° component having been through phase shifting by the 90° phase shifter 17. In this way, the received radio-frequency signal is mixed with the local oscillation signal to be modulated to the quadrature base band signals I and Q.
In the VCO 14, the local oscillation signal is stabilized to a frequency corresponding to the receiving channel, by a feed-back control performed by the PLL circuit 16. More specifically, the PLL circuit 16 compares the phase of a reference signal and the phase of the local oscillation signal having been through frequency division by the VCO 14. Then, PLL circuit 16 smoothes an error output corresponding to the phase difference so as to produce a DC tuning voltage, that is supplied to the VCO 14. The reference signal has a stable and consistent frequency, and is outputted from the oscillator 15 that is made of, for example, a crystal oscillator.
The PLL circuit 16 is supplied with a signal having a frequency corresponding to the receiving channel from, for example, an external control microcomputer. The PLL circuit 16 varies a frequency division ratio of the local oscillation signal supplied form the VCO 14, according to the supplied signal having a frequency corresponding to the receiving channel, so that the VCO 14 outputs a local oscillation signal corresponding to the receiving signal.
In this example, the gain-variable radio-frequency amplifier 3, the mixers 4 and 5, the gain-variable base band amplifiers 6 and 10, the low-pass filters 7 and 11, the amplifiers 8 and 12, the VCO 14, the PLL circuit 16, the 90° phase shifter 17 etc. constitute a frequency conversion section for performing frequency conversion upon reception of an input radio-frequency signal.
As shown in FIG. 5, the radio-frequency apparatus 1 with the described structure is subjected to delivery inspection, using a test signal transmission device 18 and a testing device 19. The test signal transmission device 18 transmits a test signal to the receiving apparatus 1 instead of the radio-frequency signal from the antenna. The test signal is supplied to the receiving apparatus 1 via the input terminal 2. The testing device 19 screens out inferior products by detecting the quadrature base band signals I and Q in terms of signal level, frequency, phase etc. and finding out whether the level of each factor is within a stipulated value.
More specifically, the following describes the case of a gain-balance test that performs an examination for finding out whether or not the output level difference of the quadrature base band signals I and Q is within a predetermined range. In this case, the test signal transmission device 18 transmits a test signal having a specific frequency; and the testing device 19 detects the signal level of the quadrature base band signals I and Q, and examines whether or not the detected level difference is within the stipulated value.
Further, in the case of a phase-difference test that performs an examination for finding out whether or not the phase difference of the quadrature base band signals I and Q is within a predetermined range, the test signal radio-frequency receiving apparatus only by externally adding some of the components. In the foregoing publication Japanese Laid-Open Patent Application Tokukai 2002-232498, that is an example of such a single chip structure, the modulation circuit (digital circuit) includes testing means, and the test is performed by supplying a sin signal via the input terminal, instead of a receiving signal.
However, in the actual wafer test, it is difficult to input a radio-frequency signal to an integrated circuit in the form of a single chip, thereby allowing the inferior chips to be carried for further processing. Further, as also disclosed in the foregoing publication Japanese Laid-Open Patent Application Tokukai 2002-232498, there has been development of a multi-chip structure in which the chip of the radio-frequency receiving apparatus is contained in a package together with a base band processing circuit etc. In this case, if an inferior chip is subjected to further processing, the whole package containing the inferior chip becomes an inferior product. For this reason, the examination at a stage of wafer state is beneficial in this structure.